The present invention relates to a rotatively driving apparatus used for such as control of a torque transmission in a four-wheel drive vehicle.
A power transmission apparatus of a related art is mounted in a four-wheel vehicle. In the four-wheel drive vehicle, a propeller shaft is interlocked with a drive system consisting of an engine and a transmission through gears and. Torque is transmitted from the propeller shaft to left and right front wheels and through a front differential gear, and the torque is also transmitted to a differential apparatus. Namely, a drive gear of the differential apparatus is coupled to the propeller shaft.
A driven gear of the differential apparatus is connected to a rear differential gear disposed between left and right rear wheels. Intermediate gears meshing with the drive gear and the driven gear hold a first gear, and the first gear meshes with a second gear. The first gear and the second gear constitute a speed increasing gear set. The second gear is coupled to a rotor of an electric motor. A stator of the electric motor is provided on a vehicle body side, and a variable resistor is connected thereto.
The torque is transmitted from the drive system to the propeller shaft. Meanwhile, the torque is transmitted to the left and right front wheels through the front differential gear. On the other hand, the torque is transmitted from the propeller shaft to the left and right rear wheels through the differential apparatus and the rear differential gear.
The transmission of the torque to the left and right rear wheels is effected from the propeller shaft through the differential apparatus in correspondence with the braking action of the gear by the electric motor corresponding to the relative magnitude of a load resistance of the variable resistor.
Thus, the front wheels serve as main driving wheels, and the rear wheels serve as auxiliary driving wheels for which variable control of the transmitted torque is effected, thereby permitting four-wheel drive running.
With the above related structure, however, the speed increasing gear set (the first and second gears) spanning the two shafts, as well as the electric motor, are offhandedly arranged, and the speed increasing gear set and the electric motor are arranged separately and are supported by the vehicle body side. Therefore, there have been problems in that the apparatus becomes large in size, and that the weight balance between the left and right sides of the four-wheel drive vehicle is deteriorated.